1. Field of the Invention
The invention relates to a hydraulic actuating arrangement, particularly for hoods, trunk lids, doors and convertible tops of vehicles, having at least one double-action working cylinder whose working chambers are connected on one side to a switchable pressure medium source by a hydraulic circuit.
2. The Prior Art
Hydraulic actuating arrangements of the noted type are known in a great number of variations whereby desired functions are realized by the type and configuration of the hydraulic circuit. For safety reasons it is proposed in most instances that in case of turn-off or malfunction of the pressure medium source, both working chambers in the hydraulic circuit are blocked by check valves or switching elements of this type whereby the piston of the working cylinder remains locked in the particular position, and whereby a convertible top, a trunk lid or the like will not move by themselves or be displaced unintentionally.
To make emergency operation or desired manual operation possible when a pressure medium source is not available, various measures have been previously disclosed whereby a manual overpressure, relative to the limiting pressure set in a pressure relief valve, applied by the user on a door to be moved, makes possible manual closing of this door. However, in all cases there remains the disadvantage to have to use the pressure (force) necessaryxe2x80x94even during intended manual operationxe2x80x94to overcome the corresponding system resistance, which is in most cases troublesome and sometimes impractical.
It is the object of the present invention to make possible, in a simple manner, emergency operation or intended manual operation of components that are normally actuated by a hydraulic actuation arrangement of the type noted above and thereby avoid the described disadvantages of such actuating arrangements.
This object is achieved with an actuating arrangement of the noted type, according to the present invention, in that both working chambers of the working cylinder can be directly connected to one another via a switchable dual-position valve. For example, this valve may be employed in relative vicinity of the particular working cylinder, parallel to the working cylinder and between the two (pressure) medium connections, which results in very short passages for the medium that is pushed from one working chamber to the other in the open position. In the closed position of the valve, other functions of the hydraulic circuit remain completely unchanged. Thereby the working cylinder is blocked in the usual manner at both sides in case of a turned-off or malfunctioning pressure medium source and the component to be displaced by the (hydraulic) actuating arrangement is held in place.
In case of a desired operation by hand of the component to be displaced, the dual-position valve may be simply switched manually or preferably by an electric switching element and, if necessary, with a lever arrangement. Thereby it is possible, for example, to open the dual-position valve with an additional lever or with the operating lever, which is combined with the trunk, during intentional manual opening of the trunk lid of an automobile without first starting the vehicle and activating the pressure medium source. After which the trunk lid may be opened practically without additional hydraulic resistance.
According to an additional embodiment of the invention, the dual-position valve is designed as a seat valve, which ensures simple and dependable operation with its simple and cost-effective component.
The invention will be described in more detail below with reference to accompanying drawings of schematically illustrated circuits of a hydraulic actuating arrangement.